The present invention relates to ink jet printbars. In particular, the invention relates to a priming device for such a printbar. Although suitable for any size printbar, the invention is particularly suited for use with a printbar comprising a full-page-width array of print dies.
Each print die contains an ink manifold providing ink to hundreds of minute capillary channels leading to the print face of the printbar. Each capillary channel is individually activated by heating a portion of the ink within the channel, thereby forming a small steam bubble which displaces and propels ink out of the channel onto a sheet of paper. Ink is supplied to each print die through sets of filters protecting the channels from contamination in the ink supply. When the printbar is filled with ink, ink will occasionally not pass through the filters and, therefore, not fill an individual print die with ink. Under other circumstances, the ink within a channel may dry or harden to the point of clogging the channel, preventing proper operation of the device. In either event, a priming operation is required to correct the flow of ink to those print dies or channels which are not functioning properly.
As a further example, ink jet printbars operate at high temperatures, often generating up to several hundred watts of heat across the printbar. Operating at these temperatures occasionally causes air ingestion into the system, requiring priming. These high temperatures may also cause air to come out of solution with the ink, resulting in the same problem. Further, rapid, repeated firing of a group of channel outlets may exceed the rate at which ink is supplied to those jets, again requiring priming. Moisture in the ink supply system may cause similar problems, requiring priming. Finally, clogging of the filters may occur during initial or refilling of the printbar ink supply, also requiring priming.
Previous priming systems have been proposed which use a vacuum conduit applied to the full width of the print die array, covering all the channel outlets along the print face. When suction is applied in these systems, however, ink is suctioned out of the channels indiscriminately, whether or not they require priming. Thus over the life of the device, significant quantities of ink are wasted during priming operations. Moreover, because suction must be applied to the full width of the print die array, strong vacuum pressure is difficult to maintain for each print die across the array.
Other priming systems have been proposed using a vacuum nozzle covering only a small group of channel outlets, where the nozzle is moved from one group of channels to another in succession. These systems suffer from "cross-talk" between groups of channel outlets in the same print die. When suction is applied to one group of channel outlets, air merely enters into an adjoining group, greatly reducing the vacuum pressure and thus the effectiveness of the priming operation.
Previous print bar systems have also used wiper blades to remove hardened and excess ink from the face of the print die array. These wiper blades are usually moistened to aid in dissolving any dried ink along the print die array. A single wet wiper or a group of wipers may be used in this capacity, and may be movably mounted to wipe across the width of the print die array. These wipers do not address the problem of clogged filters.